It is clear that the inflammatory and immune systems are critically important for the maintenance of lung structure and function in health and disease. The Pulmonary Branch has instituted a broad based program to evaluate the composition and function of the cells comprising these systems in animal models and both normal and diseased human lung. Methods have been developed to define these cell populations and evaluate their effector function. Particular attention is being paid to animal models of hypersensitivity pneumonitis, emphysema, macrophage production of factors chemotactic for neutrophils, influence of immune effector cells on connective tissue production by mesenchymal cells, and evaluation of the inflammatory and immune effector cells comprising the alveolitis of idiopathic pulmonary fibrosis and sarcoidosis.